Production of hydrofluorocarbons

ABSTRACT

A process for the production of a hydro(halo)fluorocarbon which comprises heating an  alpha -fluoroether in the vapor phase at elevated temperature.  alpha -fluoroethers are obtained by reacting a non-enolizable aldehyde with hydrogen fluoride to form an intermediate and reacting the intermediate with an alcohol or a halogenating agent. Novel  alpha -fluoroethers are also provided.

This is a continuation of application Ser. No. 07/988,679, filed on Dec.10, 1992 now abandoned.

This invention relates to a process for the production ofhydrofluorocarbons from α-fluoroethers and a process for the productionof α-fluoroethers and novel α-fluoroethers suitable for use in theproduction of hydrofluorocarbons, particularly to a process for theproduction of hydrofluoroalkanes.

In recent years chlorofluorocarbons, which are used on a large scalearound the world, have been perceived as having an adverse effect on theozone layer and/or as contributing to global warming.Chlorofluorocarbons are used, for example, as refrigerants, as foamblowing agents, as cleaning solvents and as propellants for aerosolsprays in which the variety of applications is virtually unlimited.Consequently, much effort is being devoted to finding suitablereplacements for chlorofluorocarbons which will perform satisfactorilyin the many applications in which chlorofluorocarbons are used but whichwill not have the aforementioned environmentally harmful effects. Oneapproach in the search for suitable replacements has centred onfluorocarbons which do not contain chlorine but which may containhydrogen, that is hydrofluorocarbons, of which many have been proposedas suitable replacements.

Several methods for the preparation of hydrofluorocarbons are known butmany of these methods involve the use of chlorine-containing startingmaterials and the production of chlorine-containing by-products.

The present invention provides a chlorine-free process for theproduction of hydrofluorocarbons and a process for the production ofhydrohalofluorocarbons.

According to the present invention there is provided a process for theproduction of a hydro(halo)fluorocarbon which comprises heating anα-fluoroether in the vapour phase at an elevated temperature.

By an α-fluoroether there is meant an ether having a fluorine atomattached to a carbon atom in the α-position relative to the oxygen atom,that is an ether containing the group --C--O--CF-- and thus an etherhaving the general formula R--O--CF--R¹ R², wherein R, R¹ and R² are ashereinafter defined.

We have found that α-fluoroethers of formula R--O--CF--R¹ R² may becaused to breakdown upon heating to yield a hydro(halo)fluorocarbon R--Fand a compound containing a carbonyl group, usually an aldehyde R¹ R²CO. The ether apparently breaks down by transference of an α-fluorineatom from one α-carbon atom to the other α-carbon atom to yield ahydro(halo)fluorocarbon R--F (referred to hereafter as thefluorine-exchange product). The ether may in some cases also break downby transference of an α-hydrogen atom so that a hydro(halo)fluorocarbonR--H (referred to hereafter as the hydrogen-exchange product) may alsobe produced. α-fluoro-ethers may therefore be utilised as usefulstarting materials for the production of hydro(halo)fluoroalkanes.

In the α-fluoroether R--O--CF--R¹ R², the group R may generally take anyform provided that it comprises at least one carbon atom, and the groupR may for example be saturated or unsaturated, cyclic or acyclic.Furthermore, the group R may be aliphatic or aromatic and it may be asubstituted group such as a halo-substituted group.

The process of the invention is useful in particular for the productionof hydrofluoroalkanes from ethers in which the R group is an alkyl groupwhich may comprise one, two or even more carbon atoms, say up to 6 oreven more carbon atoms. The alkyl group R will usually be a straightchain alkyl group although it may also be a branched chain alkyl group.The group R may comprise only carbon and hydrogen although it maycontain other atoms such as halogen atoms; usually the group R will be afluorinated group.

The α-fluoroether will typically be an α-fluoroalkyl ether, that is anether of formula R--O--CF--R¹ R² wherein R¹ and R² each represents ahydrogen atom or an alkyl or substituted alkyl group which may compriseone, two or even more carbon atoms, say up to 6 or even more carbonatoms, provided that where R¹ and R² both are hydrogen. R is not the--CH₂ F group. The alkyl groups R¹ and R² will usually be straight chainalkyl groups although they may also be branched chain alkyl groups. Thegroups R¹ and R² may comprise only carbon and hydrogen although they maybe substituted alkyl groups; usually the groups R¹ and R² will befluorinated groups. Typically at least one of R¹ and R² will be ahydrogen atom.

According to a preferred embodiment of the invention there is provided aprocess for the production of hydro(halo)fluoroalkanes which comprisesheating an α-fluoroether having the formula R--O--CF--R¹ R² wherein R isan alkyl or substituted alkyl group comprising from 1 to 6 carbon atomsand R¹ and R² each is H or an alkyl group containing from 1 to 6 carbonatoms.

The α-fluoroether is preferably an α-fluoromethylether, R--O--CFH₂, or atetrafluoroethylether R--O--CFH₃, since these α-fluoroethers are readilyprepared and on heating in the vapour phase to elevated temperatureyield particularly useful hydrofluorocarbons.

The α-fluoromethylether may be, for example, FCH₂ --O--CH₃(fluoromethyl-methylether), FCH₂ --O--CH₂ CF₂ H(1,1,-difluoroethyl-fluoromethyl ether), or FCH₂ --O--CH₂ CF₃(1,1,1-trifluoroethyl-fluoromethylether), which when heated in thevapour phase to elevated temperature may give the followinghydrofluoroalkanes respectively, CH₃ F, CHF₂ CH₂ F and CF₃ CH₂ F. Thetetrafluoroethylether may be, for example, CF₃ CHF--O--CH₂ CF₃ or CF₃CFH--O--CH₃ (which upon heating in the vapour phase to elevatedtemperature may yield 1,1,1,2-tetrafluoroethane) or CF₃ CFH--O--CFHCF₃or CF₃ CHF--O--CH₂ F (which upon heating in the vapour phase to elevatedtemperature may yield CF₃ CF₂ H and/or CF₃ CFH₂).

According to an embodiment of the invention there is provided a processfor the production of 1,1,1,2-tetrafluoroethane comprising heating anα-fluoroalkylether selected from the group consisting of FCH₂ --O--CH₂CF₃, FCH₂ --O--CHFCF₃, CF₃ CHF--O--CH₂ CF₃ and CF₃ CFH--O--CH₃ in thevapour phase at an elevated temperature.

According to another embodiment of the invention there is provided aprocess for the production of pentafluoroethane comprising heating CF₃CFH--O--CFHCF₃ or CF₃ CFH--O--CH₂ F in the vapour phase at an elevatedtemperature.

Heating of the α-fluoroether may advantageously be carried out in thepresence of hydrogen fluoride vapour since we have found that thepresence of hydrogen fluoride may, at least with certain α-fluoroetherstend to increase the yield of hydro(halo)fluorocarbon obtained.

Heating of the α-fluoroether may also advantageously be performed in thepresence of a catalyst. The conversion of the α-fluoroether andselectivity to the hydro(halo)fluoroalkane are dependent in particularupon the catalyst in the presence of which the α-fluoroether is heated;we have found that certain catalysts promote a high degree ofselectivity to the fluorine-exchange product whilst other catalystspromote a high degree of selectivity to the hydrogen exchange productand still other catalysts yield mixtures of both the fluorine-exchangeand hydrogen-exchange products. Furthermore, whether thefluorine-exchange product or hydrogen exchange product is promoted by aparticular catalyst is also dependent at least to some extent upon theparticular α-fluoroether. Thus with certain α-fluoroethers a particularcatalyst may promote fluorine-exchange whilst the same catalyst maypromote hydrogen-exchange with other α-fluoroethers.

It is to be understood that the process of the invention may lead to aproduct comprising a mixture of hydro(halo)fluoroalkanes from a singleα-fluoroether. Thus, for example, where the α-fluoroether is CH₂F--O--CH₂ CF₃ the product may be a mixture of CH₃ CF₃ and CF₃ CH₂ F.Furthermore, desirable mixtures of hydrofluoroalkanes may be produced,as desired, by employing mixtures of α-fluoroethers. Thus, for example,where a mixture of CH₂ F--O--CH₂ F and CF₃ CH₂ --O--CH₂ F is heated toelevated temperature, the product may comprise a mixture of CH₂ F₂, CH₃F and CF₃ CH₂ F.

The catalyst may be for example, a metal, for example a metal selectedfrom the group consisting of nickel, iron, copper and chromium, or analloy, oxide, fluoride or oxyfluoride thereof, for example chromia oralumina, aluminium or chromium fluoride, or a metal oxyfluoride.

We have found that in general the fluorine-exchange product may beproduced with very high selectivity where the catalyst employed is ametal selected from the group consisting of nickel, iron, copper orchromium and in particular where the catalyst is an alloy of at leastone of these metals. We especially prefer to employ an alloy of allthese metals, for example Hastelloy or stainless steel.

Furthermore we prefer that the alloys are air treated prior to use, thatis the alloys are heated to elevated temperature in the presence of air,for example a temperature in the range from 300° C. to 500° C.Alternatively or additionally, the catalyst pre-treatment may compriseheating the catalyst in the presence of hydrogen fluoride.

A further preferred catalyst is chromia which although it may notpromote a very high degree of selectivity to the fluorine-exchangeproduct, is a very robust catalyst. Chromia may also be given apre-treatment prior to its use.

Catalysts which in general lead to the production of thehydrogen-exchange product with a high degree of selectivity include forexample catalysts comprising zinc on chromia or zinc impregnatedchromia.

The temperature to which the α-fluoroether is heated to produce ahydro(halo)fluoroalkane is such that the α-fluoroether is in the vapourphase and the temperature will therefore depend at least to some extenton the particular α-fluoroether employed. Generally the temperature willbe at least 80° C., usually at least 200° C. and preferably at least350° C. The temperature need be no higher than about 500° C. althoughhigher temperatures, say up to about 700° C., may be used if desired.

The temperature to which the α-fluoroether is heated is also dependantat least to some extent on whether the heating is effected in thepresence or absence of a catalyst. Where the heating is effected in thepresence of a catalyst the preferred temperature is dependent on theparticular catalyst used; generally where one of the aforementionedmetals or alloys is present the temperature need not be as high as whenone of the aforementioned metals or alloys is not present.

Typically the temperature need be no higher than about 450° C. where acatalyst is used in the presence of hydrogen fluoride. Thus, forexample, where the heating is effected in the presence of stainlesssteel and hydrogen fluoride the temperature is preferably at least about250° C. and more preferably at least 300° C. but need be no higher thanabout 400° C., generally no higher than about 350° C. However, where thefluorination catalyst is chromia in the presence of hydrogen fluoridethe temperature is preferably from about 180° C. to about 320° C., morepreferably from about 200° C. to about 280° C.

The process of the invention is conveniently carried out at aboutambient pressure although superatmospheric or subatmospheric pressuresmay be used if desired. Superatmospheric pressures up to about 10 bar atlower temperatures are generally preferred since the yield ofhydro(halo)fluorocarbons is often increased under such conditions.

After completion of the reaction, the hydro(halo)fluorocarbon may beisolated from unchanged starting materials and undesired by-productsusing conventional procedures, for example distillation.

It is particularly convenient to operate the process of the invention asa continuous process wherein unchanged α-fluoroether and any hydrogenfluoride present in the hydro(halo)fluorocarbon product stream arerecycled to the reaction zone.

A particularly convenient and thus preferred general method for theproduction of the α-fluoroether is by reacting a non-enolisable aldehydewith hydrogen fluoride (in the liquid phase or in the vapour phase) andreacting the resulting intermediate with an alcohol or a halogenatingagent to form an α-fluoroether.

A non-enolisable aldehyde is required in order that the aldehyde is notpolymerised in hydrogen fluoride when the two are reacted together.

According to a preferred embodiment of the invention there is provided aprocess for the production of a hydro(halo)fluorocarbon which comprises(a) reacting a non-enolisable aldehyde with hydrogen fluoride to form anintermediate and reacting the intermediate with an alcohol or ahalogenating agent to produce an α-fluoroether and (b) treating theα-fluoroether whereby to form a hydro(halo)fluoroalkane. The treatmentof the α-fluoroether whereby to form a hydro(halo)fluoroalkane may be,for example, as hereinbefore described by heating to elevatedtemperature in the vapour phase.

The intermediate obtained by reacting the non-enolisable aldehyde withhydrogen fluoride may be reacted with the alcohol or halogenating agentin a number of ways. The aldehyde and the hydrogen fluoride may bereacted in the presence of alcohol or halogenating agent. Alternativelythe aldehyde and the hydrogen fluoride may be reacted to form anequilibrium mixture containing the intermediate and the alcohol orhalogenating agent may be added to the equilibrium mixture. In amodification of this alternative, the intermediate may be separated fromthe equilibrium mixture before it is reacted with the alcohol orhalogenating agent.

It is to be understood that the intermediate derived from thenon-enolisable aldehyde and hydrogen fluoride may itself be anα-fluoroether and that incomplete reaction of such an intermediate withthe alcohol or halogenating agent may therefore result in a mixture ofα-fluoroethers. Whilst an intermediate α-fluoroether is not the startingmaterial for use in the process for producing a hydro(halo) fluorocarbonaccording to the invention, a mixture of α-fluoroethers containingunreacted intermediate α-fluoroether is a suitable starting material foruse in the invention.

α-fluoroethers containing halogen other than fluorine, particularlychlorine or bromine, may be employed as starting materials for theproduction of hydrohalofluorocarbons containing a halogen atom otherthan fluorine. Such α-fluoroethers may be produced by reacting theintermediate derived from a non-enolisable aldehyde and hydrogenfluoride with a suitable halogenating agent to effect exchange offluorine by halogen other than fluorine. The halogenating agent may be ahalogen-containing Lewis acid such as antimony pentachloride, niobiumpentachloride, aluminium chloride and sodium bromide.

The non-enolisable aldehyde is preferably formaldehyde ortrifluoroacetaldehyde; formaldehyde is particularly preferred. In anembodiment of the invention both formaldehyde and trifluoroacetaldehydeare reacted with hydrogen fluoride to produce a mixture of CF₃CFH--O--CH₂ F and CH₂ F--O--CH₂ F. The mixture of aldehydes generates analcohol in situ and the resulting α-fluoroether mixture may be convertedto hydrofluoroalkanes. If desired, a separate alcohol may be added tothe mixture to produce further α-fluoroethers.

In the embodiment of the invention, comprising the steps of (a)producing an α-fluoroether and (b) heating the α-fluoroether in thevapour phase at an elevated temperature to form ahydro(halo)fluorocarbon, both of steps (a) and (b) employ elevatedtemperature and both may employ a catalyst so that in practice at leasta part of the α-fluoroether produced in step (a) may be converted to ahydro(halo)fluorocarbon (step b) without a change in reactionconditions. However, we have found that for optimum results differentcatalysts are preferred in step (a) and step (b); the process thencomprises operation of step (a) using a first catalyst to produce anα-fluoroether and a hydro(halo)fluorocarbon and operation of step (b)using a second catalyst to convert unreacted α-fluoroether from step (a)to the hydro(halo)fluorocarbon.

The non-enolisable aldehyde may be provided in any of its known forms.Thus formaldehyde may be provided, for example, in one of its polymericforms, paraformaldehyde or trioxane, or in its monomeric form which maybe provided, for example, from a process stream in which it has beenfreshly made, for example by the oxidation of methanol.Trifluoroacetaldehyde may be provided, for example, in its hydrated formCF₃ CH(OH)₂ or in its deydrated form CF₃ CHO.

Accordingly, whenever used herein the term non-enolisable aldehyde is tobe understood as including non-enolisable aldehydes in any of theirknown forms.

In general, where formaldehyde is used as the non-enolisable aldehyde, apolymeric form of formaldehyde such as paraformaldehyde is preferredwhere the formaldehyde is dissolved in liquid hydrogen fluoride.Paraformaldehyde and trioxane dissolve readily in liquid hydrogenfluoride and the production of the intermediate for the α-fluoroethermay be conveniently carried out by dissolving paraformaldehyde ortrioxane in liquid hydrogen fluoride at about room temperature and atabout atmospheric pressure.

The molar ratio of the non-enolisable aldehyde to hydrogen fluoride mayvary considerably, for example in the range about 1:0.5 to 1:50 but ingeneral a stoichiometric excess of hydrogen fluoride is preferred.Typically, the molar ratio of non-enolisable aldehyde to hydrogenfluoride will be in the range about 1:2 to about 1:10.

In one embodiment of the invention the non-enolisable aldehyde isreacted with hydrogen fluoride in the presence of an alcohol. In thiscase, the alcohol may be generated in situ. Thus, for example, reactionof the non-enolisable aldehyde trifluoroacetaldehyde with hydrogenfluoride is believed to yield an alcohol CF₃ CHFOH which may thencondense to give the α-fluoroether CF₃ CFH--O--CFHCF₃.

A wide range of α-fluoroethers may be produced by adding a separatealcohol. Where a separate alcohol is added, it may be added at the sametime as the hydrogen fluoride and non-enolisable aldehyde, or it may beadded subsequently to the mixture of aldehyde and hydrogen fluoride.Furthermore the alcohol may be first added to the hydrogen fluoride andthe aldehyde may then be added to this reaction mixture. Thus the orderof addition of the hydrogen fluoride, aldehyde and alcohol is notcritical.

Where the alcohol is added separately, a primary alcohol is preferredwhich may have the general formula R--OH where R is as hereinbeforedescribed. The alcohol must be inert to hydrogen fluoride and theα-fluoroether. The group R becomes the R group of the ether producedhaving the general formula R--O--CF--R¹ R², the groups R¹ and R² beingas hereinbefore described.

The group R will usually be a straight chain alkyl or substituted alkylgroup although it may also be a branched chain group. The R group maycomprise only hydrogen and carbon, for example the R group may be CH₃ orC₂ H₅. Preferably however, the R group will be fluorinated, for examplethe R group may be FCH₂ CH₂ --, HCF₂ CH₂ --, CF₃ CH₂ --, (CF₃)₂ CH--, orCF₂ HCF₂ CH₂ --. The alcohol R--OH is preferably a primary alcohol andmay be, for example, methanol, ethanol, 2-monofluoroethanol,2,2-difluoroethanol, 2,2,2-trifluoroethanol, hexafluoroisopropanol or1,1,2,2-tetrafluoropropanol. Some at least of the alcohols may begenerated in situ, for example by adding an epoxide to thenon-enolisable aldehyde/hydrogen fluoride mixture. Thus for example,2-monofluoroethanol may be generated in situ by the addition of ethyleneglycol which reacts with hydrogen fluoride to produce2-monofluoroethanol.

Where the alcohol is added separately, it may be added in similarproportions as the non-enolisable aldehyde, that is in the molar ratioof alcohol to hydrogen fluoride in the range about 1:0.5 to 1:50 but ingeneral a stoichiometric excess of hydrogen fluoride is preferred. Theoptimum proportion of alcohol added may depend upon the particularalcohol used since we have found that with certain alcohols, theaddition of too great a proportion of the alcohol leads to the formationof an undesirable acetal rather than the required α-fluoroether.Typically the molar ratio of alcohol to hydrogen fluoride will be in therange of from about 152 to about 1:10.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of the α-fluoroethers produced by the process of the inventionare novel compounds and the following α-fluoroethers are providedaccording to the invention:

Fluoromethyl-fluoroethyl ether of formula CH₂ FCH₂ OCH₂ F whose massspectrum is shown in FIG. 1 of the drawings.

Fluoromethyl-difluoroethyl ether of formula CHF₂ CH₂ OCH₂ F whose massspectrum is shown in FIG. 2 of the drawings.

Fluoromethyl-trifluoroethyl ether of formula CF₃ CH₂ OCH₂ F whose massspectrum is shown in FIG. 3 of the drawings.

Fluoromethyl-tetrafluoropropyl ether of formula CHF₂ F₂ CH₂ OCH₂ F whosemass spectrum is shown in FIG. 4 of the drawings.

Fluoroethyl-tetrafluoroethyl ether of formula CF₃ CHFOCH₂ CH₂ F whosemass spectrum is shown in FIG. 5 of the drawings.

Fluoromethyl-chloromethyl ether of formula CH₂ FOCH₂ Cl whose massspectrum is shown in FIG. 6 of the drawings.

Fluoromethyl-bromomethyl ether of formula CH₂ FOCH₂ Br whose massspectrum is shown in FIG. 7 of the drawings.

FIG. 8 of the drawings shows the mass spectrum offluoromethyl-tetrafluoroethyl ether of formula CF₃ CHFOCH₂ F. This etherhas been isolated from the mixture in which it was produced and itsboiling point was determined as 47.5° C.

The α-fluoroether may be isolated from the mixture in which it isproduced, and any by-products, before the α-fluoroether is heated toelevated temperature. The ether may be isolated, for example, by addingalkali to the mixture and heating the resulting alkaline solution, forexample up to about 50° C., in order to drive off the α-fluoroether.Alternatively the α-fluoroether may conveniently be isolated bycontacting the product stream with water at a temperature in the rangefrom about 50° C. to about 80° C. The α-fluoroether may then becollected in a cold trap or passed directly to the heating zone.

The α-fluoroether may be introduced into the heating zone in undilutedform although it is generally convenient to introduce it in conjunctionwith a diluent such as an inert carrier gas, for example nitrogen.

In the embodiment of the invention wherein the α-fluoroether isgenerated by dissolving a non-enolisable aldehyde in liquid hydrogenfluoride and reacting the resulting intermediate with an alcohol, theα-fluoroether and the hydrogen fluoride in which it is dissolved may bevaporised together into the heating zone together with any unreactedaldehyde in the solution. In this case it may be a mixture ofα-fluoroethers which is vaporised into the heating zone, so that amixture of hydrofluoroalkanes are produced by heating the mixture ofα-fluoroethers to elevated temperature. We especially prefer that theα-fluoroether and optionally hydrogen fluoride are separated from waterwhich is also produced by the reaction of the non-enolisable aldehydewith hydrogen fluoride. Thus the α-fluoroether and optionally hydrogenfluoride are preferably passed to the heating zone in the substantialabsence of water. Separation of the α-fluoroether and optionallyhydrogen fluoride from water may be achieved in any suitable manner,conveniently for example by vaporising the α-fluoroether and optionallyhydrogen fluoride from the product mixture or by contacting the productmixture with a solid drying agent. Thus for example a stream of an inertgas, for example nitrogen may be sparged through the product mixture.

Accordingly, in a further embodiment of the invention there is provideda process for the production of a hydrofluoroalkane which comprises thesteps of (a) reacting a non-enolisable aldehyde with liquid hydrogenfluoride and reacting the resulting intermediate with an alcohol toproduce an α-fluoroether, (b) separating at least some water from theproduct of step (a) and (c) passing the α-fluoroether and hydrogenfluoride from step (b) in the vapour phase into a reaction zone atelevated temperature.

In the embodiment where the non-enolisable aldehyde, hydrogen fluorideand alcohol are reacted in the vapour phase to produce theα-fluoroether, the product stream may be passed directly to a secondreaction zone, after drying if desired, optionally together withadditional hydrogen fluoride and a diluent such as nitrogen gas.

Where the α-fluoroether is generated in the liquid phase, thenon-enolisable aldehyde/hydrogen fluoride/alcohol liquid mixture ispreferably held in the liquid phase in order to prevent any prematuredecomposition of the α-fluoroether such as may occur in the vapourphase. The temperature of the liquid mixture is therefore convenientlymaintained below the boiling point of the product mixture, preferably ata temperature from about -10° C. to about 20° C.

The invention is illustrated, but not limited, by the followingexamples.

PRODUCTION OF α-FLUOROETHERS. EXAMPLE 1

24 g of anhydrous liquid hydrogen fluoride were added with cooling to 5g of trioxane and to this mixture was added 0.042 moles of methanol. Themixture was sampled immediately and analysed by Gas chromatography/MassSpectrometry. The vol % composition of the mixture was determined to be:

    ______________________________________    Component         vol % composition    ______________________________________    methanol          1.61    CH.sub.3 --O--CH.sub.2 F                      14.4    CH.sub.2 F--O--CH.sub.2 F                      66.8    CH.sub.3 --O--CH.sub.2 --O--CH.sub.3                      13.7    Trioxane          3.4    ______________________________________

EXAMPLE 2

The procedure of example 1 was repeated except that 0.073 moles ofethanol were employed. The volume % composition of the mixture wasdetermined to be:

    ______________________________________    Component            vol % composition    ______________________________________    ethanol              5.7    CH.sub.3 CH.sub.2 --O--CH.sub.2 F                         17.8    CH.sub.2 F--O--CH.sub.2 F                         36.5    CH.sub.3 CH.sub.2 --O--CH.sub.2 --O--CH.sub.2 CH.sub.3                         35.2    Trioxane             2.1    ______________________________________

EXAMPLE 3

The procedure of example 1 was repeated except that 0.073 moles of2-fluoroethanol were employed. The volume % composition of the mixturewas determined to be:

    ______________________________________    Component           vol % composition    ______________________________________    2-fluoroethanol     5.7    CH.sub.2 FCH.sub.2 --O--CH.sub.2 F                        29.0    CH.sub.2 F--O--CH.sub.2 F                        45.0    CH.sub.2 FCH.sub.2 --O--CH.sub.2 --O--CH.sub.2 CH.sub.2 F                        10.0    Trioxane            4.7    ______________________________________

EXAMPLE 4

The procedure of example 1 was repeated except that 0.073 moles of2,2-difluoroethanol were employed. The volume % composition of themixture was determined to be:

    ______________________________________    Component           vol % composition    ______________________________________    2,2-difluoroethanol 4.7    CF.sub.2 HCH.sub.2 --O--CH.sub.2 F                        59.2    CH.sub.2 F--O--CH.sub.2 F                        30.8    CF.sub.2 HCH.sub.2 --O--CH.sub.2 --O--CH.sub.2 CF.sub.2 H                        3.6    Trioxane            0.0    ______________________________________

EXAMPLE 5

The procedure of example 1 was repeated except that 0.073 moles of2,2,2-trifluoroethanol were employed. The volume % composition of themixture was determined to be:

    ______________________________________    Component            vol % composition    ______________________________________    2,2,2-trifluoroethanol                         11.1    CF.sub.3 CH.sub.2 --O--CH.sub.2 F                         62.3    CH.sub.2 F--O--CH.sub.2 F                         17.0    CF.sub.3 CH.sub.2 --O--CH.sub.2 --O--CH.sub.2 CF.sub.3                         9.5    Trioxane             0.0    ______________________________________

EXAMPLE 6

The procedure of example 1 was repeated except that 0.042 moles of1,1,2,2-tetrafluoropropanol were employed. The weight % composition ofthe mixture was determined to be:

    ______________________________________                              vol %    Component                 composition    ______________________________________    1,1,2,2-tetrafluoropropanol                              7.85    CF.sub.2 HCF.sub.2 CH.sub.2 --O--CH.sub.2 F                              59.6    CH.sub.2 F--O--CH.sub.2 F 29.3    CF.sub.2 HCF.sub.2 CH.sub.2 --O--CH.sub.2 --O--CH.sub.2 CF.sub.2 CF.sub.2    H                         1.4    Trioxane                  1.9    ______________________________________

EXAMPLE 7

0.5cms³ of trifluoroacetaldehyde in the form of its hydrate CF₃ CH(OH)₂was added to 6 cms³ of anhydrous liquid hydrogen fluoride and themixture was analysed by nuclear magnetic resonance. Analysis indicatedthat the ether CF₃ CHF--O--CHFCF₃ was the major product.

EXAMPLE 8

6 cms³ of anhydrous liquid hydrogen fluoride were added with cooling to1.25 g of paraformaldehyde and to this mixture was added 0.5 cms³ of CF₃CH(OH)₂. Gas chromatography and Mass spectrometry indicated that theethers CF₃ CHF--O--CH₂ F and CH₂ F--O--CH₂ F were the main products.

DECOMPOSITION OF ETHERS EXAMPLE 9

The product mixture of example 1 was sparged with nitrogen at a flowrate of 50cms³ per minute and the sparged mixture was fed to an Inconeltube packed with 200cms³ of Hastelloy C mesh and heated to an elevatedtemperature. The off gas was scrubbed with water and analysed by Gaschromatography. At 257° C. the composition of the off gas was:

    ______________________________________    Component.       % v/v.    ______________________________________    CH.sub.3 F       19.2    CH.sub.2 F.sub.2 60.8    CH.sub.2 F--O--CH.sub.2 F                     20.0    ______________________________________

EXAMPLE 10

The procedure of example 9 was repeated except that the product mixtureof example 5 was sparged with nitrogen and the Inconel tube was packedwith 200cms³ of chromia pellets. At 350° C. the composition of the offgas was:

    ______________________________________    Component.       % v/v    ______________________________________    CH.sub.3 F       31.5    CH.sub.2 F.sub.2 46.6    CF.sub.3 CH.sub.2 F                     13.9    CF.sub.3 CH.sub.3                     0.4    CH.sub.2 F--O--CH.sub.2 F                     1.0    Others           6.6    ______________________________________

EXAMPLE 11

The procedure of example 9 was repeated except that the product mixtureof example 6 was sparged with nitrogen. Mass spectrometry indicated that1,1,2,2,3-pentafluoropropane was the major product.

EXAMPLE 12

The procedure of example 9 was repeated except that the product mixtureof example 4 was sparged with nitrogen and the Inconel tube was packedwith 115 ml (70 g) stainless steel rings which had been air-treated byheating the rings to 350° C. in a stream of air for 4 hours. At 350° C.,the composition of the off gas was:

    ______________________________________    Component.         % v/v    ______________________________________    CH.sub.2 F.sub.2   4.5    CF.sub.2 HCH.sub.2 F                       23.8    CF.sub.2 HCH.sub.2 OH                       4.2    CH.sub.2 F--O--CH.sub.2 F                       44.5    CF.sub.2 HCH.sub.2 --O--CH.sub.2 F                       21.1    Others             1.9    ______________________________________

EXAMPLE 13

0.4 g (0.012 moles) of methanol were added to 1.7 g (0.021 moles) ofBFME with stirring and cooling 10 ml (0.5 moles). HF or 98% H₂ SO₄ wereadded and the mixture stirred at room temperature prior to analysis bygas chromotography and mass spectrometry.

    ______________________________________    Found:               % (by GC)    ______________________________________    Bis-fluoromethyl ether (BFME)                         55.0    Fluoro methyl ether  27.3    Methanol             7.05    Bis(fluoromethoxy)methane                         0.62    Dimethoxy methane    8.0    Trioxane             1.64    ______________________________________

EXAMPLE 14

Trioxane (10 g, 0.33 moles) was added to HF (48 g, 2.4 moles) withstirring. Ethanol (1.72 g, 0.037 moles) was carefully added dropwise,with stirring and cooling.

Analysis of the products by mass spectrometry showed the main componentsto be BFME and the acetal diethoxymethane. Fluoromethyl ethyl ether, C₂H₅ OCH₂ F, was also identified.

EXAMPLE 15

2-fluoroethanol (4.678, 0.073 moles) was added to a mixture of trioxane(5 g, 0.167 moles) in HF (24 g, 1.2 moles). After stirring for 30minutes, the products were analysed:

    ______________________________________    Found                % (by GC)    ______________________________________    BFME                 32.1    Fluoromethyl methyl ether                         1.4    2-fluoroethanol      58.5    Fluoromethyl 2-fluoroethyl ether                         6.3    Bis(fluoromethoxy)methane                         0.06    Trioxane             1.0    ______________________________________

EXAMPLE 16

1.5 g (0.018 moles) 2,2-difluoroethanol was added to 1.7 g (0.021 moles)BFME. 0.25 ml (0.0125 moles) HF or 98% H₂ SO₄ were added and the mixturestirred for 20-30 minutes before sampling

    ______________________________________    Found:                 % (by GC)    ______________________________________    BFME                   31.8    Fluoromethyl2,2-difluoroethyl ether                           27.3    2,2dilfuoroethanol     1.6    Bis(fluoromethoxy)methane                           3.1    CHF.sub.2 CH.sub.2 OCH.sub.2 OCH.sub.2 F                           3.9    Trioxane               1.2    ______________________________________

EXAMPLE 17

3.7 g (0.037 moles) of 2,2,2-trifluoroethanol were added to 3.4 g (0.021moles) BFME with cooling and stirring. 0.3 ml (0.015 moles) HF or 98% H₂SO₄ were added and the mixture sampled after stirring at roomtemperature for 20-30 minutes.

    ______________________________________    Found:                 % (by GC)    ______________________________________    BFME                   15.9    Fluoro methyl2,2,2-trifluoroethyl ether                           63.4    Trifluoroethanol       1.5    CF.sub.3 CH.sub.2 OCH.sub.2 OCH.sub.2 F                           5.8    CF.sub.3 CH.sub.2 OCH.sub.2 OCH.sub.2 OCH.sub.2 F                           12.3    ______________________________________

EXAMPLE 18

10 g of 1H 1H 3H-tetrafluoropropanol were added to a mixture of 6 gtrioxane in 20 g HF. After stirring the mixture was analysed.

    ______________________________________    Found:                   % (by GC)    ______________________________________    BFME                     23.6    Fluoromethyl 2,2,3,3, tetrafluoropropylether                             67.0    1H, 1H, 3H-tetrafluoropropanol                             4.3    Bis(Fluoromethoxy)methane                             1.3    CF.sub.3 HCF.sub.2 CH.sub.2 OCH.sub.2 OCH.sub.2 F                             2.15    Trioxane                 1.5    ______________________________________

EXAMPLE 19

Trioxane (1 g, 0.033 moles) was added to HF (5 g, 0.25 moles) and themixture cooled. Hexafluoroisopropanol (2.38 g, 0.0142 moles) was addedand the products analysed after 5 minutes stirring.

    ______________________________________    Found:             % (by GC)    ______________________________________    BFME               22.2    (CF.sub.3).sub.2 CHOCH.sub.2 F                       4.9    Hexafluoroisopropanol                       71.6    (CF.sub.3).sub.2 CHOCH.sub.2 OCH.sub.2 F                       1.3    ______________________________________

EXAMPLE 20

SbCl5 (1.1 g, 0.0051 moles) was added to a cooled vessel containing BFME(2.0 g, 0.0244 moles) and stirred.

The contents of the head above the solution were analysed after 1 hour.

The experiment was then repeated, with the addition of 2 g HF.

    ______________________________________                       % (by GC)    Found:               without HF                                   with    ______________________________________    HF    BFME                 44.6      29.8    Difluoromethane      19.8      18.1    Methyl chloride      1.7       2.8    Chlorofluoromethane  12.4      17.0    Dichloromethane      3.2       8.0    Chloromethyl fluromethylether                         17.6      22.4    Bis(chloromethyl)ether                         0.5       1.65    ______________________________________

EXAMPLE 21

NbCl₅ (0.3 g, 0.0016 moles) was added to BFME (1.7 g, 0.021 moles) andthe head space analysed after stirring for about an hour.

    ______________________________________    Found:              % (by infra red)    ______________________________________    BFME                88.6    Difluoromethane     0.034    Methyl fluoride     0.012    Fluoromethyl methyl ether                        0.57    Chloromethyl fluromethylether                        10.5    Bis(chloromethyl)ether                        0.28    ______________________________________

EXAMPLE 22

Aluminium chloride (0.5 g, 0.06 moles) was added to BFME (2.0 g, 0.0244moles) with stirring. The head space was analysed by infra redspectroscopy. The experiment was then repeated with the further additionof HF (0.2 g, 0.01 moles).

    ______________________________________                     % (by infra red)    Found:             without HF                                 with HF    ______________________________________    BFME               97.57     87.0    Difluoromethane    0.044     0.17    Methyl fluoride    --        0.014    Fluoro methyl ether                       0.024     0.056    Dichloromethane    --        0.09    Bis(fluoromethoxy)methane                       0.17      0.1    Chloromethyl fluromethyl-                       2.19      12.56    ether    ______________________________________

EXAMPLE 23

10 g of paraformaldehyde were added to 48 g HF and the mixture stirred.15 g of sodium bromide were added, 5 g at a time. On addition of thefinal 5 g, the mixture separated into two layers. The bottom layer wasanalysed and found to contain a mixture of BFME, bromomethylfluoromethyl ether and bis(bromomethyl) ether.

The experiment was repeated using BFME and HBr. HBr was bubbled throughBFME (4 g, 0.049 moles) for 5-10 minutes. One layer was observed; thiswas analysed by mass spectroscopy and found to contain BFME andbromomethyl fluoromethyl ether as the main products, with a small amountof bis(bromomethoxy)methane also present.

EXAMPLES 24-27

In these examples ethers were sparged directly from trioxane/HFequilibrium mixture+alcohol and as such were co-fed with BFME. Reactionproducts therefore contain CH₂ F₂ and CH₃ F from this source.

EXAMPLE 24

The following composition was sparged over a Hastelloy C (20 ml)catalyst held in a 1' tube at 257° C.

    ______________________________________                   Percentage    ______________________________________    CH.sub.3 OH      1.61    BFME             66.8    CH.sub.3 OCH.sub.2 F                     14.4    Dimethoxymethane 13.7    Trioxane         3.4    ______________________________________

The off gases were scrubbed with water prior to analysis by GC.

    ______________________________________           Found % (by GC)    ______________________________________           CH.sub.3 F                 19.2           CH.sub.2 F.sub.2                 60.8           BFME  20.0    ______________________________________

EXAMPLE 25

The following composition was sparged over stainless steel rings (115 l)at 324° C.

    ______________________________________                    %    ______________________________________    BFME              14.5    2,2 difluoroethanol                      42.3    Fluoromethyl 2,2- 41.4    difluoroethyl ether    ______________________________________

    ______________________________________    Found             % (by GC)    ______________________________________    CH.sub.2 F.sub.2  4.4    CH.sub.2 FCHF.sub.2                      23.5    BFME              44.05    Fluoromethyl methyl-                      1.9    ether    2,2 difluoroethanol                      4.1    Fluoromethyl 2,2,-                      20.9    difluoroethyl ether    ______________________________________

EXAMPLE 26

The following composition was sparged chromia catalyst (200 ml) at 350°C.

    ______________________________________                     %    ______________________________________    CF.sub.3 CH.sub.2 OCH.sub.2 F                       61.3    BFME               16.8    Trifluoroethanol   11.0    CF.sub.3 CH.sub.2 OCH.sub.2 OCH.sub.2 F                       9.4    Trioxane           1.6    ______________________________________

    ______________________________________    Found         % (by GC)    ______________________________________    CH.sub.3 F    31.5    CH.sub.2 F.sub.2                  46.6    BFME          1.0    CH.sub.3 CF.sub.3                  0.4    CF.sub.3 CH.sub.2 F                  13.9    Others        6.6    ______________________________________

EXAMPLE 27

The ether/BFME was separated from equilibrium mixture and CF₂ HCF₂ CH₂OH and the following composition sparged over Hastalloy C (120 ml) at259° C.

    ______________________________________                     % (by infra red)    ______________________________________    BFME               4.1    Fluoromethyl 2,2,3,3-                       68.5    tetrapropyl ether    Bis(fluoromethoxy)-                       2.1    ether    1H, 1H, 3H tetra-  4.3    fluoropropanol    CF.sub.2 HCF.sub.2 CH.sub.2 OCH.sub.2 OCH.sub.2 F                       20.8    ______________________________________

    ______________________________________    Found            % (by infra red)    ______________________________________    Fluoromethyl 2,2,3,3-                     60.3    tetrafluoropropyl-    ether    1H, 1H, 3H tetra-                     1.0    fluoropropanol    CH.sub.3 F       1.2    CH.sub.2 F.sub.2 0.7    CH.sub.2 FCF.sub.2 CH.sub.2 F                     12.8    Others           24.0    ______________________________________

EXAMPLE 28

Fluoral hydrate (0.5 g, 0.0043 moles) was added to a mixture ofparaformaldehyde (1.25 g, 0.0417 moles) and HF (6.0 g, 0.3 moles) andthe mixture analysed after stirring for 30 minutes.

    ______________________________________    Found           % (by mass spec)    ______________________________________    BFME            59.5    Fluoral hydrate 0.37    CF.sub.3 CHFOCH.sub.2 F                    27.8    CF.sub.3 CHFOCH.sub.2 CH.sub.3                    0.29    CH.sub.2 FOCH.sub.2 OCH.sub.2 F                    1.5    Trioxane        1.79    ______________________________________

EXAMPLE 29

Methanol (0.6 g, 0.0187 moles) was added to fluoral hydrate (1.7 g,0.0146 moles) with stirring and cooling. HF (2.2 g, 0.11 moles) wasadded and the reaction product analysed after stirring.

    ______________________________________    Found          % (by infra red)    ______________________________________    Methanol       3.6    Fluoral hydrate                   46.4    Methyl 1,2,2,2-                   48.3    tetrafluoroethyl-    ether    Ethyl 1,2,2,2- 1.7    tetrafluoroethyl    ether    ______________________________________

EXAMPLE 30

Ethanol (1.9 g, 0.041 moles) was added to fluoral hydrate (2.6 g, 0.022moles) with stirring and cooling. HF (2.0 g, 0.1 moles) was then addedand the mixture analysed after 30 minutes stirring.

    ______________________________________    Found          % (by infra red)    ______________________________________    Ethanol        94.9    Fluoral hydrate                   1.6    Ethyl 1,2,2,2- 3.65    tetrafluoroethyl-    ether    ______________________________________

EXAMPLE 31

2-fluoroethanol (3.0 g, 0.047 moles) was added to fluoral hydrate (4.3g, 0.037) with stirring and cooling. HF (5.0 g, 0.25 moles) was addedand the mixture was analysed after stirring for 30 minutes.

    ______________________________________    Found              % (infra red)    ______________________________________    Fluoral hydrate        65.1    Methanol               3.5    Acetaldehyde           2.8    Trifluoroethanol       0.8    2-fluoroethanol        27.2    2'-fluoroethyl-    1,2,2,2 tetrafluoro-   0.62    ethyl ether    ______________________________________

EXAMPLE 32

PREPARATION OF FLUOROMETHYL-2,2,2-TRIFLUOROETHYL ETHER

100 g of anhydrous HF were added to 20 g of trioxane in a plastic bottlecooled in crushed ice. To the solution was added 50 g oftrifluoroethanol. The resulting solution was added slowly to 500 ccs ofcrushed ice to produce an aqueous and an organic layer. The organiclayer was separated off and distilled to give 99% pure ether (G.C/MS.,NMR).

PREPARATION OF CATALYST FOR DECOMPOSITION OF ETHER

The catalysts were sieved to give particles in the range 1.18 mm to 0.25mm and then packed into a stainless steel tube. They were prefluorinatedby sparging HF with nitrogen at a flow rate of 50 ccs per min andpassing the vapours over the catalyst at 350° C. for 4 hours.

DECOMPOSITION OF ETHER

5 g of ether were dissolved in 15 g of HF and sparged over the catalystwith nitrogen at a flow rate of 20 cc per min. The off gas was scrubbedwith water and analysed by G.C.

    ______________________________________    Catalyst    ______________________________________    AlF3 @ 400° C.                   unchanged ether                                  4.7%    10 cc          134a           49%                   143a           6.7%                   32             22.5%                   41             9.2%                   CO             5.1%    LaF3 @ 500° C.                   unchanged ether                                  75.7%    1 cc           134a           1.8%                   143a           5.5%                   32             11.4%                   41             1.9%                   CO             3.0%    90% Fe 203     unchanged ether                                  16.3%    10% Cr 203     134a           43%    @ 500° C.                   143a           4.7%    10 cc          32             7.7%                   41             9.3%                   CO             16.4%    42% CuO        unchanged ether                                  <1%    58% Cr2O3      134a           52%    @ 400° C.                   143a           26%    10 cc          32             8%                   41             3%                   CO             7%    ______________________________________

EXAMPLE 33

PREPARATION OF FLUOROMETHYL-1,2,2,2-TETRAFLUOROETHYL ETHER, CF₃ CHFOCH₂F

Trioxane (10 g, 0.33 moles) was added to anhydrous HF (150 g, 7.5 moles)with stirring and cooling. Fluoral hydrate (10 g, 0.086 moles) was addedto the mixture which was analysed after 24 hours.

    ______________________________________    Found (% by mass spectrometry)    ______________________________________    BFME               46.6    CF.sub.3 CHFOCH.sub.2 F                       41.05    CF.sub.3 CHFOCH.sub.2 OCH.sub.2                       5.8    Unknown            5.2    CF.sub.3 CHFOCH.sub.3                       1.3    ______________________________________

EXAMPLE 34

Ethanol (3.24 g, 0.0704 moles) was added to a cooled, stirred mixture oftrioxane (5 g, 0.166 moles) in HF (24 g, 2,2 moles). The products wereanalysed by GC and mass spectrometry.

    ______________________________________    Found (% by mass spec.)    ______________________________________    BFME                36.5    Diethoxy ethane     35.2    Fluoromethyl ether ether                        17.8    Ethanol             5.7    BFMM                2.8    Trioxane            2.06    ______________________________________

EXAMPLE 35

Hexafluoroisopropanol (2.38 g, 0.0142 moles) was added to a cooled,stirred mixture of trioxane (1 g, 0.0133 moles) in HF (5 g, 0.25 moles).After stirring for 5 minutes, the mixture was analysed by massspectrometry.

    ______________________________________    Hexafluoroisopropanol                       71.6    BFME               22.2    (CF.sub.3).sub.2 CHOCH.sub.2 F                       4.9    (CF.sub.3).sub.2 choch.sub.2 och.sub.2 f                       1.3    ______________________________________

We claim:
 1. A process for the production of 1,1,1,2-tetrafluoroethanewhich comprises heating an α-fluoroether in the vapour phase at anelevated temperature in the presence of hydrogen fluoride and a catalystselected from the group consisting of nickel, iron, copper and chromiumor an alloy, oxide, fluoride or oxyfluoride theref, said α-fluoroetherbeing selected from the group consisting of FCH₂ --O--CH₂ CF₃, FCH₂--O--CHFCF₃, CH₃ CHF--O--CH₂ CF₃ and CF₃ CHF--O--CH₃.
 2. A process asclaimed in claim 1 wherein the α-fluoroether is heated at a pressure offrom 1 to 10 bar.
 3. A process as claimed in claim 1 wherein the1,1,1,2-tetrafluoroethane product is separated from the product streamwhich is then recycled to the reaction zone.